Production of synthetic gas (“syngas”) from a carbon-containing feedstock using gasification and other processes is known. During gasification, the carbon-containing feedstock, which can be natural gas, coal, biomass, organic waste, crude oil, oil residues and/or the like, is fed to a gasifier. In the gasifier, the carbon-containing feedstock undergoes a set of chemical reactions at high temperatures in the presence of controlled amounts of oxygen and/or steam. Syngas, a gas mixture, results from this process.
The main components of syngas can include varying ratios of hydrogen, carbon monoxide, and carbon dioxide. Other constituents of syngas can include methane, carbon dioxide, water vapor, sulfur compounds, ammonia, nitrogen, hydrogen cyanide and the like.
Syngas is often further processed and purified in one or more downstream processes to produce a usable syngas product. Conventional processing and purification of a syngas feedstock can include the production of synthetic natural gas (“SNG”), conversion of carbon monoxide to hydrogen gas, removing carbon dioxide and/or sulfur, production of methanol, and/or purifying to remove other undesirable components. Purifying can result in a waste gas, which can include valuable hydrocarbons (including olefins and liquid hydrocarbons) which, in turn, may fuel the gasification process.
Syngas also includes arsenic, selenium, and other trace contaminants. Some of these trace contaminants, including arsenic and selenium, are particularly deleterious and can poison the catalysts in downstream processes, resulting in deactivation of the catalyst. For example, both arsenic and selenium may poison the catalysts used in the downstream water-gas shift reaction which adjusts the hydrogen-to-carbon monoxide (H2/CO) ratio.
Accordingly, there is a need to remove certain trace contaminants, including arsenic and selenium, from the syngas feedstock to avoid deactivation of catalysts used in downstream processes.